The invention herein relates generally to control systems and, more particularly, to antiskid brake control systems of the type presently utilized in the aircraft industry. It has been found that on some aircraft brakes that the coefficient of friction of the brake disks themselves may vary over a range of 5 to 1. Presently known antiskid systems cannot provide efficient braking over this entire range. The problem inherent in presently existing antiskid systems is that such systems respond to skid depth to control brake pressure rather than brake torque when the true desire of such systems is to control brake torque. In aircraft braking systems, the relationship between torque and brake pressure may change significantly for different braking conditions. For example, at a low energy condition, the desired foot-pounds of braking torque may be achieved at 400 psi of braking pressure, but under a high energy condition, such as on a rejected takeoff, the same foot-pounds of brake torque may require 2,000 psi of brake pressure. Accordingly, there is a significant tremendous change in system gain between the low and high energy conditions.
In the past, it has been found that it is extremely difficult to obtain good braking efficiency over the whole range of possible system gains. While the problem might be resolved if a reliable torque transducer and mounting were developed and the antiskid system made responsive thereto, such has not been the case. The industry is thus confronted with the fact that in many applications the relationship between brake torque and brake pressure is represented by a family of curves mostly dependent upon braking energy or the energy of the body being stopped.
It is therefore advantageous to provide an antiskid system in which the antiskid gain may be modified as a function of brake torque and brake pressure. In such a manner, the antiskid system will be equally sensitive and responsive in both low and high energy conditions and varying degrees thereof.